• bonding analysis;
  • density functional calculations;
  • gallium;
  • germanium;
  • metalloid clusters

After publication of this Communication, the authors learned about theoretical and experimental studies of four-membered cyclic compounds containing a B2E2 moiety (E = N, P, As) which possess a similar bonding situation as in their Ge2Ga2 species.13 In particular, the isolated and structurally characterized 1,3-dibora-2,4-diphosphoniocyclobutane-1,3-diyl which has a cyclic B2P2 fragment exhibits a transannular B[BOND]B π bond without a B[BOND]B σ bond.1 Thus, the Ge2Ga2 compound described in the Communication is not the first example of a stable species which exhibits a π bond between two atoms without a σ bond. The authors are grateful to Didier Bourissou for drawing their attention to these precedents.